First, the disclosures of U.S. Pat. Nos. 3,772,180 and 3,847,775 are incorporated in this present disclosure by reference. The two incorporated disclosures are duplicates of each other, their claims separately covering the method and apparatus of their inventions. The general organization of the disclosures of these two patents is followed in the present disclosure. A mixture of oil and water represents the medium passed sequentially through the DC and AC type of electrostatic fields generated by the electrodes. The mixture may be more generally defined as that of a polar liquid finely dispersed and in an immiscible non-polar liquid. Of course, interchangeably, the disclosure can refer to either a two-phase mixture of immiscible polar and non-polar liquids, or a mixture of oil and water. In both events, the problem arises with the reduction in the dielectric strength of these mixtures. The effectively AC electrostatic field is generated between the electrodes and the ground reference, while the second electrostatic field is maintained between the electrodes. The mixture of liquids is first flowed through the AC type of field and, secondly, through the DC field for progressive coalescence of the dispersed liquid droplets.
Subsequent to the formation of the disclosures of the incorporated patents, emulsions have been discovered as having variable dielectric strengths. This mode of expression contrasts with the previous reference to varying electrical conductivity of the emulsions. It now appears more appropriate to use the term dielectric strength as compatible with the characteristics of the electrostatic fields.
There has been a nagging problem in reducing the invention of the incorporated patents to practice. Specifically, when flowing emulsions of decreasing dielectric strength through the two electrostatic fields, the DC electrostatic field between the energized electrodes correspondingly decreases to ineffective values. Various arrangements to maintain the strength of the DC field have been employed, but no arrangement has satisfactorily obviated the simultaneous loss of AC field strength. Fortunately, there is prior art which exemplifies the inadequate solution to this problem.
U.S. Pat. No. 4,049,535 discloses one arrangement to maintain the DC field while the load impedance of the emulsion is low. However, the addition of the full-wave rectifier, utilizing a grounded center-tap transformer, eliminates the AC field. The opposing voltages generated cancel each other, resulting in zero voltage between the combined electrodes and ground. This arrangement destroys the valuable AC field required in the sequential application of the two electrostatic fields. A circuit arrangement is needed which will sustain a DC field of significant strength without significantly reducing the strength of the AC field.